And that is exactly what is wrong with this event. You shouldn't have to play a guessing game within a game to get a max prize. How many people play this game that don't read forums or the wiki and are going to miss out on a fully upgraded Colossus because they didn't know they had to pick the best ratio players every single time they threw the ball?Sounds like you chose your players based on what was in the chest and/or the highest DS% regardless of yard/football ratio. You went for the short term rewards and will now fall short of the full prize without diamonds.
If someone completes the event, the event should be balanced so they should have enough upgrades for a maxed Colossus.